This invention relates to fluid brake systems for vehicles.
A conventional vehicle fluid brake system includes a master cylinder which is connected by a piping system to brake calipers or wheel cylinders at each wheel. Movement of master cylinder pistons by a brake pedal actuator develops fluid pressure which is transmitted through the piping system to the wheel calipers or cylinders. Braking systems conventionally include a power source which utilizes either engine vacuum and atmospheric pressure or hydraulic pressure to provide power assist or "boost" to the master cylinder in applying fluid force to the braking system.
When a brake pedal is depressed, force is transferred by a push rod to the master cylinder primary piston which moves forward. Under normal conditions the combination of fluid pressure and the force of the primary piston's spring moves a secondary piston forward at the same time. When the pistons move forward, fluid is displaced until front and rear wheel brake linings contact the rotors or drums. Subsequently, hydraulic pressure is built up and transmitted to the front and rear wheels causing the brakes to be applied.
When the brake pedal actuator is released, fluid is forced back through the piping system to the master cylinder. Excess fluid returns to a reservoir which is generally mounted on top of the master cylinder.
Three typical types of general brake systems are two-channel, three-channel, and four-channel systems. Two-channel systems include diagonal split systems and front/rear split systems. In a diagonal split system the left front and right rear brakes are connected with one master cylinder piston forming a channel. The right front and left rear brakes are connected with the other master cylinder piston forming another channel. A typical front/rear split brake system includes one master cylinder piston that is connected with the front brakes and another that is connected with the rear brakes. In a three-channel arrangement the brake system is split into independent left/front and right/front channels and a combined rear channel. In a four-channel arrangement the brake system is divided into a separate channel for each of the four wheel brakes.
The art has adapted conventional vehicle fluid brake systems as thus far described to sophisticated control mechanisms which represent a combination of hydraulic and electrical control and provide advanced braking functions. One such mechanism, an anti-lock braking system (ABS), typically modulates the fluid pressure delivered to a vehicle wheel brake to prevent the vehicle wheel brake from locking up in certain braking conditions. Another such mechanism, traction control (TC), typically modulates the fluid pressure delivered to a vehicle wheel brake to prevent spinning of a powered vehicle wheel, thereby maximizing the traction that is exerted by the vehicle's drive wheels. When a vehicle is being braked or accelerated a typical ABS or TC system operates to individually maximize the force between each wheel and the road surface to maximize vehicle braking or acceleration.
The integration of ABS and TC into vehicle braking systems has presented the challenge to provide a competitive, integrated braking system that is adaptable to providing normal braking, anti-lock braking and traction control operation for the various types of braking systems.